The present invention relates generally to data communication systems and more particularly relates to a system for transporting Ethernet frames over Very high speed Digital Subscriber Lines (VDSL).
There is a growing need among both individuals and enterprises for access to a commonly available, cost effective network that provides speedy, reliable services. There is high demand for a high-speed data network, one with enough bandwidth to enable complex two-way communications. Such an application is possible today if, for example, access is available to a university or a corporation with sufficient finances to build this type of network. But for the average home computer user or small business, access to high speed data networks is expensive or simply impossible. Telephone companies are therefore eager to deliver broadband services to meet this current explosion in demand.
One of the problems is that millions of personal computers have found their place in the home market. Today, PCs can be found in over 60% of all United States households, many of which have more than one computer networked together, and over 50% of United States teenagers own computers. Virtually every PC sold today is equipped with a modem, enabling communication with the outside world via commercial data networks and the Internet. Currently, people use their PCs to send and receive e-mail, to access online services, to participate in electronic commerce and to browse the Internet. The popularity of the Internet is such that there are over 100 million users around the globe. These figures indicate that in the past few years the personal computer has fueled a dramatic increase in data communications and the corresponding demands on the data networks that carry the traffic.
The Internet serves as a good example of the increased demands that have been placed on data networks. At first, Internet access consisted of text only data transfers. Recently, with the popularity of the World Wide Web (WWW) and the construction of numerous sites with high quality content, coupled with the development of Internet browsers such as Mosaic, Netscape Navigator and Microsoft Internet Explorer, the use of graphics, audio, video and text has surged on the Internet. While graphics, audio and video make for a much more interesting way to view information as opposed to plain text, bandwidth consumption is significantly higher. A simple background picture with accompanying text requires approximately 10 times the bandwidth needed by text alone. Real-time audio and streaming video typically need even more bandwidth. Because of the increased requirement for bandwidth, activities such as browsing home pages or downloading graphics, audio and video files can take a frustratingly long period of time. Considering that the multimedia rich World Wide Web accounts for more than one quarter of all Internet traffic, it is easy to see why the demand for bandwidth has outpaced the supply. In addition, the creative community is pushing the envelope by offering audio and full motion video on numerous sites to differentiate themselves from the millions of other sites competing for user hits.
As use of the Internet and online services continues to spread, so does the use of more complex applications, such as interactive video games, telecommuting, business to business communications and videoconferenceing. These complex applications place severe strains on data networks because of the intensive bandwidth required to deliver data-rich transmissions. For example, a telecommuter who requires computer aided design (CAD) software to be transported over the data network requires a high-bandwidth data pipeline because of the significant size of CAD files. Similarly, a business to business transaction in which large database files containing thousand of customer records are exchanged also consumes large amounts of bandwidth. The same is true for users seeking entertainment value from sites offering high quality video and audio. The lack of available bandwidth in today""s data networks is the primary barrier preventing many applications from entering mainstream use. Just as processing power limited the effectiveness of early PCs, bandwidth constraints currently limit the capabilities of today""s modem user.
Most computer modem users access data through the standard telephone network, known as plain old telephone service (POTS). Equipped with today""s speediest modems, dial up modems on a POTS network can access data at a rate of 28.8, 33.6 or 56 Kbps. Dial up modem transmission rates have increased significantly over the last few years, but POTS throughput is ultimately limited to 64 Kbps. While this rate may be acceptable for some limited applications like e-mail, it is a serious bottleneck for more complex transactions, such as telecommuting, videoconferenceing or full-motion video viewing. To illustrate, full motion video compressed, using the Motion Picture Entertainment Group (MPEG)-2 standard requires a data stream of approximately 6 Mbps, or roughly 208 times the throughput of a 28.8 Kbps modem. Thus, using today""s dial up modems, it would take more than 17 days to capture two hours of video. As bandwidth demands continue to grow, providers search for better ways to offer high speed data access. Further complicating the problem is the need to deliver all these complex services at an affordable price.
Today""s most popular data access method is POTS. But as discussed previously, POTS is limited when it comes to large data transfers. An alternative to POTS currently available is Integrated Services Digital Network (ISDN). In the past few years, ISDN has gained momentum as a high-speed option to POTS. ISDN expands data throughput to 64 or 128 Kbps, both from the network to the home and from the home back to the network, and can be technically made available throughout much of the United States and in many other parts of the globe. Similar to POTS, ISDN is a dedicated service, meaning that the user has sole access to the line preventing other ISDN users from sharing the same bandwidth. ISDN is considered an affordable alternative, and in general, ISDN is a much better solution for applications such as Web browsing and basic telecommuting. However, like POTS, it severely limits applications such as telecommuting with CAD files and full-motion video viewing. The latter requires roughly 39 times the throughput than that provided by ISDN. Multichannel multipoint distribution service (MMDS), a terrestrial microwave wireless delivery system, and direct broadcast satellite (DBS), such as DirecTv and US Satellite Broadcasting (USSB), are wireless networks. They both deliver high bandwidth data steams to the home, referred to as downstream data, but neither has a return channel through which data is sent back over the network, referred to as upstream data. Although it is a relatively affordable system to deploy for broadcast applications, because it requires no cable wires to be laid, it falls short in interactive access. In order to use a wireless system for something as basic as e-mail, an alternate technology such as a telephone line must be used for the upstream communications.
Another network delivery system is asymmetric digital subscriber line (ADSL). Offering a downstream capacity of 6 Mbps or more to the home, ADSL has the downstream capacity to handle the most complex data transfers, such as full motion video, as well as an upstream capacity of at least 500 Kbps. However, due to its limitation of downstream bandwidth capacity, it essentially is a single service platform. Also, since it has to overcome the challenge of reusing several thousand feet of twisted pair wiring, the electronics required at each end of the cable are complex, and therefore currently very expensive.
Hybrid fiber coax (HFC), a network solution offered by telephone and cable companies, is yet another option for delivering high bandwidth to consumers known in the art. However, HFC has limitations. HFC networks provide a downstream capacity of approximately 30 Mbps, which can be shared by up to 500 users. Upstream bandwidth is approximately 5 Mbps and also is shared. A disadvantage with HFC is that shared bandwidth and limited upstream capacity become serious bottlenecks when hundreds of users are sending and receiving data on the network, with service increasingly impaired as each user tries to access the network.
It is a current trend among telephone companies around the world to include existing twisted pair copper loops in their next generation broadband access networks. Hybrid Fiber Coax (HFC), a shared access medium well suited to analog and digital broadcast, comes up short when utilized to carry voice telephony, interactive video and high speed data communications at the same time.
Fiber to the home (FTTH) is still prohibitively expensive in the marketplace that is soon to be driven by competition rather than costs. An alternative is a combination of fiber cables feeding neighborhood Optical Network Units (ONUs) and last leg premises connections by existing or new copper. This topology, which can be called fiber to the neighborhood (FTTN), encompasses fiber to the curb (FTTC) with short drops and fiber to the basement (FTTB), serving tall buildings with vertical drops.
One of the enabling technologies for FTTN is very high rate digital subscriber line (VDSL). VDSL is an emerging standard that is currently undergoing discussion in ANSI and ETSI committees. The system transmits high-speed data over short reaches of twisted pair copper telephone lines, with a range of speeds depending upon actual line length.
The VDSL standard as provided by the VDSL Draft Specification being drafted by the ANSI T1E1.4 Technical Subcommittee, provides guidelines for the transmitter and receiver within the VDSL modem. The connection between the VDSL modem and the CPE specifies a number of signals including TxData, RxData, RxErr, TxCLK, RxCLK and TxSOC and RxSOC. The latter two signals, i.e., TxSOC and RxSOC, provide an indication of the start of the VDSL frame to the CPE for both transmission and reception.
In accordance with the VDSL Draft Specification, it is intended that the Tx and Rx SOC signals be used by the CPE to synchronize the transmission and reception of the data to and from VDSL modem. In the case of transporting Ethernet data over the VDSL facility, a problem arises, however, when attempting to synchronize Ethernet frames to VDSL frames. The problem with using these Tx and Rx SOC signals is that the VDSL frame comprises a fixed number of bytes, e.g., 256 bytes, whereas the Ethernet frame may vary from 64 to 1518 bytes. Designing and implementing the circuitry, e.g., state machines, timing and framing circuits, etc., to perform the protocol matching, i.e., sync timing between Ethernet frames and VDSL frames is very complicated and hence expensive to implement.
It is desirable to have a means of transporting Ethernet frame data over a VDSL transport facility that does not require the complicated circuitry and state machines when utilizing the SOC signals provided by the VDSL modem.
The present invention is an apparatus for and method of encapsulating Ethernet frames over a Very high speed Digital Subscriber Line (VDSL) transport facility. The VDSL frames are transmitted over a point to point VDSL link where they are subsequently extracted and forwarded as standard Ethernet frames.
The VDSL facility transport system comprises an Ethernet to VDSL Customer Premises Equipment (CPE) to in communication with a DSL Access Multiplexor (DSLAM) over a VDSL transport facility. The DSLAM is typically located at the curb or before the xe2x80x98last milexe2x80x99 in a subscriber loop. The Ethernet to VDSL CPE functions to receive a 10BaseT Ethernet signal and encapsulate the Ethernet frame into a VDSL frame for transmission over the VDSL facility. Likewise, the Ethernet to VDSL CPE also functions to receive a VDSL signal, extract Ethernet frames therefrom and output them as standard 10BaseT Ethernet signals.
The DSLAM is adapted to receive VDSL frames, extract Ethernet frames therefrom and generate and output a standard Ethernet signal. Likewise, the DSLAM is also adapted to receive standard Ethernet frames from an Ethernet input signal and encapsulate them in VDSL frames for transmission over the VDSL facility.
In accordance with the invention, the SOC signals provided by the VDSL are not utilized in transmitting the Ethernet frame data over the VDSL facility. Ethernet frames are encapsulated within VDSL frames and transmitted on the wire pair without regard to the state of the SOC signals. This overcomes the problems associated with synchronizing the transmission of the Ethernet data with the SOC signals.
Both the CPE and DSLAM comprise an Ethernet encapsulation/extraction (EEE) unit which functions to store and forward the Ethernet frames in both directions. The EEE unit comprises interface circuitry to couple the transmit and receive frame data to and from the VDSL channel.
The present invention also provides a method of providing the receiving station an indication of the start of a VDSL frame. A preamble having certain desirable characteristics such as good autocorrelation properties is used by the receiving station to identify the start of a VDSL frame. To further ensure that a detected start of frame is valid, the length field of the VDSL frame is examined.
The receiving station performs a check to determine whether the preamble pattern detected is actually a preamble or is Ethernet data within the payload of the VDSL frame. The length field contains 16 bits allowing for 65,536 combinations but only 1518xe2x88x9264=1454 of them are valid since the payload of the VDSL frame carries only Ethernet frame data which can only range from 64 to 1518 bytes. Thus, the length field is checked to further narrow the chance of a wrong synchronization.
There is therefore provided in accordance with the present invention an apparatus for encapsulating and extracting Ethernet frames to and from a Very high speed Digital Subscriber Line (VDSL) facility, including an Ethernet transceiver for receiving and transmitting Ethernet frames from and to an Ethernet source, an Ethernet encapsulation/extraction (EEE) unit coupled to the Ethernet transceiver and operative to store Ethernet frames received therefrom for subsequent forwarding encapsulated within VDSL frames over the VDSL facility, the EEE unit operative to extract Ethernet frames received from the VDSL facility and subsequently store and them for forwarding to the Ethernet transceiver and the VDSL transceiver for receiving and transmitting VDSL frames from and to the VDSL facility.
The Ethernet encapsulation/extraction unit comprises Ethernet input circuitry coupled to the transmit portion of the Ethernet source and operative to convert the Tx serial input bitstream to a parallel stream of Tx bytes, Ethernet output circuitry coupled to the receive portion of the Ethernet source and operative to convert a parallel stream of Rx bytes into a Rx serial bitstream, VDSL output circuitry coupled to the transmit portion of the VDSL facility and operative to transfer VDSL frames ready for transmission to the VDSL transceiver, VDSL input circuitry coupled to the receive portion of the VDSL facility and operative to receive VDSL frames from the VDSL transceiver, a memory unit for storing data received from the Ethernet input circuitry and the VDSL input circuitry and a data processor coupled to the Ethernet input circuitry, Ethernet output circuitry, the VDSL output circuitry and the VDSL input circuitry, the data processor operative to store and forward data received via the Ethernet input circuitry to the VDSL output circuitry, the data processor operative to store and forward data received via the VDSL input circuitry to the Ethernet output circuitry.
The Ethernet transceiver comprises a 10BaseT Ethernet transceiver operative to communicate with a 10BaseT Ethernet source.
There is also provided in accordance with the present invention a Digital Subscriber Line Access Multiplexor (DSLAM) for encapsulating and extracting Ethernet frames to and from one or more Very high speed Digital Subscriber Line (VDSL) facilities, including a plurality of VDSL transceivers for receiving and transmitting VDSL frames from and to the VDSL facilities, an Ethernet transceiver for receiving and transmitting Ethernet frames from and to an Ethernet source, an Ethernet encapsulation/extraction (EEE) unit coupled to the plurality of VDSL transceivers and operative to extract Ethernet frames received from the VDSL facility and subsequently store and them for forwarding to the Ethernet transceiver, the EEE unit operative to store Ethernet frames received from the Ethernet source for subsequent forwarding encapsulated within VDSL frames over the VDSL facilities and an Ethernet switch operative to provide switching functions for one or more bidirectional Ethernet frame streams to and from of the EEE and the Ethernet transceiver.
The Ethernet transceiver comprises a 100BaseT Ethernet transceiver operative to communicate with a 100BaseT Ethernet source. The Ethernet switch comprises an Ethernet switch adapted to switch between a plurality of 10BaseT Ethernet channels and at least one 100BaseT Ethernet source.
There is further provided in accordance with the present invention, a method of encapsulating Ethernet frames onto a Very high speed Digital Subscriber Line (VDSL) facility, the method comprising the steps of receiving Ethernet frames from an Ethernet source, storing the Ethernet frames for subsequent forwarding, encapsulating the previously stored Ethernet frames within VDSL frames and transmitting the VDSL frames over the VDSL facility.
In addition, there is provided in accordance with the present invention, a method of extracting Ethernet frames from a Very high speed Digital Subscriber Line (VDSL) facility, the method comprising the steps of receiving VDSL frames from the VDSL facility, extracting Ethernet frames from the VDSL frames received, storing the Ethernet frames for subsequent forwarding and forwarding the Ethernet frames to an Ethernet source.